# Full text of "Handbook Of Chemical Engineering - I"

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```POWER GENERATION AND TRANSMISSION
A given value of ns implies a given value of w, the peripheral coefficient, or ratio u -r- *\/2gh where u = peripheral speed of runner rim, feet per second, at the actual speed. Thus, for Allis-Chalmers reaction wheels:
Type	A	B	C	D	E	F	G	H
ns ............	13.55	20.30	29.40	40.70	51.7-60.5	72.00	82 00	92.50
771      ....	0.585	0.625	0 665	0.70	0 75	0 80	0 77	0 815

If a wheel of type C were used under 400 ft. head at 1,200 r.p.m., the power developed at the runner would be  (29.4 X 4005'4 -s- 1,200)2 = 1,920.    With an efficiency   of 0.80, the brake horsepower is 1,920 X 0.8 = 1,536.    The volume of water required per second is Q = (550  X P)/62.4ft cu. ft., or 42.4 cu. ft. for the assumed conditions.     The peripheral   speed is  0.665 V2gh= 0-665 X 20 X 8.02 = 106.7feet per second and the wheel diameter  is 106.7 X 12 -5- 207r= 20.4 in.    Runners of high specific speed are usually less efficient at normal load than those of low specific speed, but hold up better in power and efficiency  at  over-gate  flows,   and  are therefore best adapted for variable heads,
especially in low-head plants. The efficiency at part-load is of no importance unless water is stored, and storage in low-head plants is rare. High specific speeds imply large wheel diameters for a given head and rotative speed: the range of diameters (inches) being from l,070-\A/n to l,530\//i/7i for specific speeds from 13}-£ to 92J^-Since P = n«2. ft'^ -r n2, high specific speeds also increase the .power of a wheel to be operated at fixed head arid rotative speed.
Tangential (Impulse) Wheels.—The tangential water wheel is somewhat less efficient than the reaction turbine at full load, but its